Multi-gate device and method of fabrication thereof

ABSTRACT

A semiconductor device includes a fin extending from a substrate. The fin has a source/drain region and a channel region. The channel region includes a first semiconductor layer and a second semiconductor layer disposed over the first semiconductor layer and vertically separated from the first semiconductor layer by a spacing area. A high-k dielectric layer at least partially wraps around the first semiconductor layer and the second semiconductor layer. A metal layer is formed along opposing sidewalls of the high-k dielectric layer. The metal layer includes a first material. The spacing area is free of the first material.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 14/994,399, entitled “MULTI-GATE DEVICE AND METHODOF FABRICATION THEREOF,” filed Jan. 13, 2016, which is herebyincorporated by reference in its entirety

BACKGROUND

The semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower cost. Despite groundbreaking advances in materials andfabrication, scaling planar device such as the conventional MOSFET hasproven challenging. To overcome these challenges, circuit designers arelooking to novel structures to deliver improved performance. One avenueof inquiry is the development of three-dimensional designs, such as afin-like field effect transistor (FinFET). A FinFET can be thought of asa typical planar device extruded out of a substrate and into the gate. Atypical FinFET is fabricated with a thin “fin” (or fin structure)extending up from a substrate. The channel of the FET is formed in thisvertical fin, and a gate is provided over (e.g., wrapping around) thechannel region of the fin. Wrapping the gate around the fin increasesthe contact area between the channel region and the gate and allows thegate to control the channel from multiple sides. This can be leveragedin a number of way, and in some applications, FinFETs provide reducedshort channel effects, reduced leakage, and higher current flow. Inother words, they may be faster, smaller, and more efficient than planardevices.

Continued FinFET scaling also presents critical challenges. For example,as FinFETs are scaled down through various technology nodes, gate stacksusing gate dielectric materials having a high dielectric constant (e.g.,high-k dielectrics) have been implemented. In implementing high-k/metalgate stacks, it is important to properly scale an equivalent oxidethickness (EOT) of the gate structure to improve device performance.However, an interfacial layer may be required between the gatedielectric layer (e.g., HfO₂) and the channel, which also contributes tothe EOT of the gate structure. Furthermore, the interfacial layer mayaffect the flat band voltage and/or threshold voltage of FinFETs.Therefore, as the scale of FinFETs decreases, the thickness and/oruniformity of the interfacial layer become more and more critical.

Therefore, what is needed is an improved multi-gate structure andfabrication method.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A and 1B are flow charts of a method of fabricating asemiconductor device or portion thereof according to one or more aspectsof the present disclosure.

FIGS. 2A, 2B, 2C, 2D, and 2E are cross-sectional views of a portion of asemiconductor device according to an embodiment of the presentdisclosure.

FIGS. 3A, 3B, 3C, and 3D are cross-sectional views of a portion of asemiconductor device according to an embodiment of the presentdisclosure.

FIGS. 4A, 4B, 4C, 4D, 4E, and 4F are cross-sectional views of a portionof a semiconductor device according to an embodiment of the presentdisclosure.

FIG. 5A is an isometric view of a portion of a semiconductor deviceaccording to an embodiment of the present disclosure. FIG. 5B is across-sectional view of a portion of a semiconductor device according toan embodiment of the present disclosure.

FIG. 6 is a cross-sectional view of a portion of a semiconductor deviceaccording to an embodiment of the present disclosure.

FIGS. 7A, 7B, 7C, 7D, and 7E are cross-sectional views of a portion of asemiconductor device according to an embodiment of the presentdisclosure. FIG. 7F is an isometric view of a portion of a semiconductordevice according to an embodiment of the present disclosure.

FIG. 8A is a cross-sectional view of a portion of a semiconductor deviceaccording to an embodiment of the present disclosure. FIG. 8B is anisometric view of a portion of a semiconductor device according to anembodiment of the present disclosure.

FIGS. 9A, 9B, and 9C are cross-sectional views of a portion of asemiconductor device according to an embodiment of the presentdisclosure.

FIGS. 10A, 10B, and 10C are cross-sectional views of a portion of asemiconductor device according to various embodiments of the presentdisclosure.

FIGS. 11A, 11B, and 11C are cross-sectional views of a portion of asemiconductor device according to various embodiments of the presentdisclosure.

FIGS. 12A, 12B, 12C, and 12D are cross-sectional views of a portion of asemiconductor device according to some embodiments.

FIGS. 13A, 13B, and 13C are graphs illustrating maximum scavengingdistances of interfacial layers as a function of spacing distancebetween adjacent channel semiconductor layers and channelcross-sectional profiles according to various embodiments.

FIGS. 14A, 14B, and 14C are cross-sectional views of a portion of asemiconductor device according to some embodiments.

FIG. 15 is a perspective view of a portion of a semiconductor deviceaccording to some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

It is also noted that the present disclosure presents embodiments in theform of multi-gate transistors or fin-type multi-gate transistorsreferred to herein as FinFET devices. Such a device may include a P-typemetal-oxide-semiconductor FinFET device or an N-typemetal-oxide-semiconductor FinFET device. The FinFET devices may begate-all-around (GAA) devices, Omega-gate (Ω-gate) devices, Pi-gate(Π-gate) devices, dual-gate devices, tri-gate devices, bulk devices,silicon-on-insulator (SOI) devices, and/or other configuration. One ofordinary skill may recognize other examples of semiconductor devicesthat may benefit from aspects of the present disclosure.

Illustrated in FIG. 1A is a method 100 of semiconductor fabrication forforming fin elements including semiconductor layers over a substrate.Referring to FIG. 1A, the method 100 begins at block 102, where asubstrate is provided. Referring to the example of FIG. 2A, in anembodiment of block 102, a substrate 202 is provided. In someembodiments, the substrate 202 may be a semiconductor substrate such asa silicon substrate. The substrate 202 may also include othersemiconductors such as germanium (Ge), silicon carbide (SiC), silicongermanium (SiGe), or diamond. Alternatively, the substrate 202 mayinclude a compound semiconductor and/or an alloy semiconductor. Thesubstrate 202 may include various layers, including conductive orinsulating layers formed on a semiconductor substrate. The substrate 202may include various doping configurations depending on designrequirements as is known in the art. For example, different dopingprofiles (e.g., n wells, p wells) may be formed on the substrate 202 inregions designed for different device types (e.g., n-type field effecttransistors (NFET), p-type field effect transistors (PFET)). Thesuitable doping may include ion implantation of dopants and/or diffusionprocesses. The substrate 202 typically has isolation features (e.g.,shallow trench isolation (STI) features) interposing the regionsproviding different device types. Further, the substrate 202 mayoptionally include an epitaxial layer (epi-layer), may be strained forperformance enhancement, may include a silicon-on-insulator (SOI)structure, and/or have other suitable enhancement features.

Referring to FIG. 1A, the method 100 proceeds to block 104, where astrain relaxed buffer (SRB) layer 204 is grown over the substrate 202.Referring to the example of FIG. 2A, an SRB layer 204 is grown over thesubstrate 202 using atomic layer deposition (ALD), chemical vapordeposition (CVD), high-density plasma CVD (HDP-CVD), physical vapordeposition (PVD) and/or other suitable deposition processes. The SRBlayer 204 may be different in composition from the substrate 202 inorder to create lattice strain at the interface with the substrate 202.For example, in some embodiments, the substrate 202 includes silicon andis substantially free of Germanium while the SRB layer 204 includesSiGe. In various such examples, the SRB layer 204 has a germaniumconcentration in the range of about 25 atomic percent to about 100atomic percent.

Referring to FIG. 1A, after forming the SRB layer 204 over the substrate202 at block 104, various embodiments of the method 100 to form the finelements over the substrate may be used. In one embodiment, the method100 proceeds to block 106, where a stack including semiconductor layersare formed over the substrate. Referring to the example of FIG. 2A, astack 212 of semiconductor layers is formed over the substrate 202. Inembodiments that include an SRB layer 204 disposed on the substrate 202,the stack 212 of semiconductor layers may be disposed on the SRB layer204. The stack 212 of semiconductor layers may include alternatinglayers of different compositions. For example, in some embodiments, thestack 212 includes semiconductor layers 206 of a first compositionalternating with semiconductor layers 208 of a second composition.Although three semiconductor layers 206 and three semiconductor layers208 are shown, it is understood that the stack 212 may include anynumber of layers of any suitable composition with various examplesincluding between 2 and 10 semiconductor layer 206 and between 2 and 10semiconductor layers 208. As explained below, the different compositionsof the layers in the stack 212 (e.g., semiconductor layers 206 andsemiconductor layers 208) may be used to selectively process some of thelayers. Accordingly, the compositions may have different oxidationrates, etchant sensitivity, and/or other differing properties.

In some embodiments, either of the semiconductor layers 206 and 208 mayinclude silicon. In some embodiments, either of the semiconductor layers206 and 208 may include other materials such as Ge, a compoundsemiconductor such as silicon carbide, gallium arsenide, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide,an alloy semiconductor such as SiGe, GaAsP, AlinAs, AlGaAs, InGaAs,GaInP, and/or GaInAsP, or combinations thereof. In some embodiments, thesemiconductor layers 206 and 208 may be undoped or substantiallydopant-free (i.e., having an extrinsic dopant concentration from about 0cm⁻³ to about 1×10¹⁷ cm⁻³), where for example, no doping is performedduring the epitaxial growth process. Alternatively, the semiconductorlayers 208 may be doped. For example, the semiconductor layers 206 or208 may be doped with a p-type dopant such as boron (B), aluminum (Al),indium (In), and gallium (Ga) for forming a p-type channel, or an n-typedopant such as phosphorus (P), arsenic (As), antimony (Sb), for formingan n-type channel.

The semiconductor layers 206 and 208 may have thicknesses chosen basedon device performance considerations. In some embodiments, thesemiconductor layer 206 has a thickness range of about 2-15 nanometers(nm). In some embodiments, the semiconductor layers 206 of the stack 212may be substantially uniform in thickness. In some embodiments, thesemiconductor layer 208 has a thickness range of about 2-15 nm. In someembodiments, the semiconductor layers 208 of the stack 212 aresubstantially uniform in thickness.

By way of example, growth of the layers of the stack 212 may beperformed by a molecular beam epitaxy (MBE) process, a metalorganicchemical vapor deposition (MOCVD) process, and/or other suitableepitaxial growth processes.

Referring to FIG. 1A, the method 100 proceeds to block 110, where finelements are formed. Referring to the example of FIG. 2C, fin elements214A and 214B may be fabricated using suitable processes includingphotolithography and etch processes. In some embodiments, a resist 216is formed over the stack 212 and patterned using a lithography process.The patterned resist 216 may then be used to protect regions of thesubstrate 202, and layers formed thereupon, while an etch process formstrenches 209 in unprotected regions through the resist 216, through thestack 212, and into the SRB layer 204. The remaining portions of thestack 212 become fin elements 214A and 214B that include thesemiconductor layers 206 and 208. In some embodiment, the patterns inresist 216 are controlled so as to result in a desired width W of thefin elements 214A and 214B. The width W may be chosen based on deviceperformance considerations. In some embodiments, the width W issubstantially the same as a thickness of the semiconductor layer 206 or208, and has a range of about 2-15 nm.

Referring to FIG. 1A, the method 100 proceeds to block 110, whereisolation features are formed. Referring to the example of FIG. 2D, adielectric material, such as silicon oxide, may be deposited into thetrenches 209 to form isolation features 210. A chemical mechanicalplanarization (CMP) process may be performed to planarize a top surfaceof the device 200. In some embodiments, the CMP process used toplanarize the top surface of the device 200 the isolation features 210may also serve to remove the resist from the fin elements 214A and 214B.In some embodiments, removal of the resist may alternatively beperformed by using a suitable etching process (e.g., dry or wetetching).

Referring to FIG. 1A and FIG. 2E, the method 100 proceeds to block 112,where the isolation features 210 are recessed. Referring to the exampleof FIG. 2E, the isolation features 210 interposing the fin elements 214Aand 214B are recessed, thereby leaving the fin elements 214A and 214Bextending above the isolation features 210. In some embodiments, therecessing process may include a dry etching process, a wet etchingprocess, and/or a combination thereof. In some embodiments, a recessingdepth is controlled (e.g., by controlling an etching time) so as toresult in a desired height H of the exposed upper portion of the finelements 214A and 214B. The height H may be chosen based on deviceperformance considerations. In some embodiments, the height H is betweenabout 8 nm and 300 nm.

Referring back to FIG. 1A, in another alternative embodiment of themethod 100, after forming the SRB layer 204 over the substrate 202 atblock 104, the method 100 proceeds to block 114, where isolationfeatures are formed over the substrate. Referring to the example of FIG.3A, isolation features 210 may be formed using suitable processesincluding photolithography, etch, and deposition processes, and aportion of the SRB layer 204 interposes the isolation features 210.

Referring to FIGS. 1A and 3B, the method 100 the proceeds to block 116,where trenches 302 between isolation features 210 are formed. Referringto the example of FIG. 3B, the portion of the SRB layer 204 interposingthe isolation features 210 is at least partially etched to form trenches302.

Referring to FIGS. 1A and 3C, the method 100 then proceeds to block 118,where stacks 212 including semiconductor layers 206 and 208 are formedin the trenches 302, and fin elements 214A and 214B are formed.

Referring to FIGS. 1A and 3D, the method 100 then proceeds to block 120,where the isolation features 210 are recessed to provide the finelements 214A and 214B extending above a top surface of the isolationfeatures 210.

Referring back to FIG. 1A, in yet another alternative embodiment of themethod 100, after forming the SRB layer 204 over the substrate 202 atblock 104, the method 100 proceeds to block 122, where a hard mask isformed over the substrate. Referring to the example of FIG. 4A, a hardmask 402 is formed over the SRB layer 204. In some embodiments, the hardmask 402 may include a dielectric such as a semiconductor oxide, asemiconductor nitride, and/or a semiconductor carbide.

Referring to FIGS. 1A and 4B, the method 100 proceeds to block 124,where the hard mask 402 is patterned and etched. Referring to FIGS. 1Aand 4C, the method 100 proceeds to block 126, where isolation features210 are formed adjacent to the remaining portions of mask 402 usingsuitable processes including photolithography, etch, and depositionprocesses. Referring to FIGS. 1A and 4D, the method 100 proceeds toblock 128, where an etch process may be used to remove the remainingportions of mask 402, thereby forming trenches 302 between isolationfeatures 210. Referring to FIGS. 1A and 4E, the method 100 proceeds toblock 130, where stacks 212 including semiconductor layers 206 and 208are grown in the trenches 302 to form fin elements 214A and 214B.Referring to FIGS. 1A and 4F, the method 100 proceeds to block 132,where the isolation features 210 are recessed to provide the finelements 214A and 214B extending above a top surface of the isolationfeatures 210.

In some embodiments, forming the fin elements 214A and 214B may furtherinclude a trim process to decrease the width W and/or the height H ofthe fin elements 214A and 214B. The trim process may include wet or dryetching processes. The height H and width W of the fin elements 214A and214B may be chosen based on device performance considerations.

Referring now to FIG. 1B, illustrated is a method 150 of semiconductorfabrication for forming multi-gate devices. The method 150 begins atblock 152, where a substrate includes fin elements includingsemiconductor layers stacked over the substrate is received. The finelements may be formed by an embodiment of the method 100 describedabove or other suitable method known in the art. Referring to theexample of FIGS. 5A and 5B, a substrate 202 including fin elements 214Aand 214B including semiconductor layers 206 and 208 is provided. In someembodiments, the fin element 214A is a portion of N-type metal-oxidesemiconductor (NMOS) elements, and fin element 214B is a portion ofP-type metal-oxide semiconductor (PMOS) elements. As illustrated in FIG.5B, the fin element 214A extends from a first region 500 (also referredto as an NMOS region) of the substrate 202, and the fin element 214Bextends from a second region 501 (also referred to as a PMOS region) ofthe substrate 202.

Referring now to FIGS. 1B, 5A, and 5B, the method 150 then proceeds toblock 154 where dummy gate structures 506 are formed on the substrate202. The dummy gate structure 506 may be replaced at a later processingstage by a high-K dielectric layer (HK) and metal gate electrode (MG) asdiscussed below. In some embodiments, the dummy gate structure 506 isformed over the substrate 202 and is at least partially disposed overthe fin elements 214A and 214B. The portion of the fin elements 214A and214B underlying the dummy gate structure 506 may be referred to as thechannel region 512. The dummy gate structure 506 may also define asource/drain region 510 of the fin elements 214A, 214B, for example, asthe portion of the fin elements 214A and 214B adjacent to and onopposing sides of the channel region 512.

Referring now to FIG. 5B, illustrated is a cross section of a portion ofan embodiment of device 200 along the A-A′ line of FIG. 5A. Asillustrated in the example of FIG. 5B, the dummy gate structure 506 mayinclude a capping layer 502 formed on the fin elements 214A, 214B. Insome embodiments, the capping layer 502 may include SiO₂, siliconnitride, a high-K dielectric material or other suitable material. Invarious examples, the capping layer 502 may be deposited by a CVDprocess, a subatmospheric CVD (SACVD) process, a flowable CVD process,an ALD process, a PVD process, or other suitable process. By way ofexample, the capping layer 502 may be used to prevent damage to the finelements 214A and 214B by subsequent processing (e.g., subsequentformation of the dummy gate structure). In some embodiments, the dummygate structure 506 may include a dummy gate electrode layer 504 formedover the capping layer 502 on the fin elements 214A, 214B. In someexamples, the dummy gate electrode layer 504 may include polycrystallinesilicon (polysilicon). In some embodiments, the dummy gate structure 506may include a dielectric layer 508 formed over the dummy gate electrodelayer 504.

In some embodiments, the dummy gate structure 506 may be formed byvarious process steps such as layer deposition, patterning, etching, aswell as other suitable processing steps. Exemplary layer depositionprocesses includes CVD (including both low-pressure CVD andplasma-enhanced CVD), PVD, ALD, thermal oxidation, e-beam evaporation,or other suitable deposition techniques, or combinations thereof. Informing the dummy gate structure 506 for example, the patterning processincludes a lithography process (e.g., photolithography or e-beamlithography) which may further include photoresist coating (e.g.,spin-on coating), soft baking, mask aligning, exposure, post-exposurebaking, photoresist developing, rinsing, drying (e.g., spin-dryingand/or hard baking), other suitable lithography techniques, and/orcombinations thereof. In some embodiments, the etching process mayinclude dry etching (e.g., RIE etching), wet etching, and/or otheretching methods.

In some embodiments, a gate spacer may be formed on sidewalls of thedummy gate structure 506. The gate spacer may include one or moredielectric materials such as silicon nitride, silicon oxide, siliconcarbide, silicon oxycarbide (SiOC), silicon oxycarbon nitride (SiOCN),other materials, or a combination thereof. The spacer layer may includea single layer or a multi-layer structure. The spacer layer may beformed by chemical oxidation, thermal oxidation, ALD, CVD, and/or othersuitable methods.

Referring now to FIGS. 1B and 6, the method 150 then proceeds to block156 where source/drain features are formed. Referring now to FIG. 6,illustrated is a cross section of a portion of an embodiment of device200 along the B-B′ line of FIG. 5A in the source/drain region 510. Thesource/drawn features may be formed by performing an epitaxial growthprocess that provides an epitaxy material cladding the portions of thesemiconductor layers 206 and/or 208 in the fin elements 214A and 214B'ssource/drain regions 510. In the example of FIG. 6, source/drainfeatures 602 are formed over the substrate 202 on the fin elements 214Aand 214B adjacent to and associated with the dummy gate structure 506.

In various embodiments, the source/drain features 602 may include Ge,Si, GaAs, AlGaAs, SiGe, GaAsP, SiP, or other suitable material. In someembodiments, source/drain features 602 may be in-situ doped during theepi process. For example, in some embodiments, the source/drain features602 may be doped with boron. In some embodiments, the source/drainfeatures 602 may be doped with carbon to form Si:C source/drainfeatures, phosphorous to form Si:P source/drain features, or both carbonand phosphorous to form SiCP source/drain features. In some embodiments,the source/drain features 602 are not in-situ doped, and instead animplantation process is performed to dope the source/drain features 602.

In some embodiments, at block 156, after forming the source/drainfeatures, an etch-stop layer (e.g., a contact etch stop layer (CESL)704) and various dielectric layers (e.g., an inter-layer dielectric(ILD) layer 702) are formed on the substrate 202. Referring to FIG. 7A,illustrated is a cross section of a portion of an embodiment of device200 along the C-C′ line (along the fin element 214B) of FIG. 5A. In someembodiments, a CESL 704 is formed over the gate spacer 710 and dummygate structure 506. In some examples, the CESL 704 includes a siliconnitride layer, silicon carbon nitride layer, a silicon oxynitride layer,and/or other materials known in the art. The CESL 704 may be formed byALD, PECVD, or other suitable deposition or oxidation processes. Aninter-layer dielectric (ILD) layer 702 may be formed over the CESL 704.In some embodiments, the ILD layer 702 includes materials such astetraethylorthosilicate (TEOS) oxide, un-doped silicate glass, or dopedsilicon oxide such as borophosphosilicate glass (BPSG), fused silicaglass (FSG), phosphosilicate glass (PSG), boron doped silicon glass(BSG), and/or other suitable dielectric materials. The ILD layer 702 mayformed by a PECVD process, a flowable CVD (FCVD) process, or othersuitable deposition technique.

Referring to the example of FIG. 7B, in an embodiment, after the CESL704 and the ILD layer 702 are deposited, a planarization process, suchas a chemical mechanical planarization (CMP) process, may be performedto expose a top surface of the dummy gate structure 506. The CMP processmay remove portions of the ILD layer 702 and CESL 704 overlying thedummy gate structure 506 and may planarize a top surface of the device200. In addition, the CMP process may remove portions of the dummy gatestructure 506 to expose the dummy gate electrode layer 504.

Referring to the example of FIG. 7C, in some embodiments, an etchprocess may be performed to the ILD layer 702 to remove a top portion ofthe ILD layer 702, thereby forming openings 706 on top of the ILD layer702. Referring to the example of FIG. 7D, a dielectric material (e.g.,silicon nitride) may be deposited over the substrate 202 to fill theopenings 706, thereby forming a dielectric layer 708.

Referring to the example of FIGS. 7E and 7F, illustrated are across-sectional view and an isometric view of the device 200 after a CMPprocess is performed to planarize a top surface of the device 200respectively. In some embodiments, the CMP process may remove portionsof the dielectric layer 708 to expose the dummy gate electrode layer 504from a top surface of the device 200.

Referring now to FIGS. 1B, 8A, and 8B, the method 150 then proceeds toblock 158 where the dummy gate structure 506 is removed to expose thechannel regions of the fin elements. Referring to FIGS. 8A and 8B, theremoval of the dummy gate structure 506 forms an opening 804 thatexposes the channel regions 512 of the fin elements 214A and 214B. In anembodiment, block 158 includes one or more etching processes, such aswet etching, dry etching, or other etching techniques.

Referring to FIGS. 1B and 9A, the method then proceeds to block 160where portions of selected semiconductor layers in the channel regionsare removed through the opening 804. Block 160 may include a firstremoval process to remove selected semiconductor layers (e.g.,semiconductor layers 206) in the NMOS region 500 and a second removalprocess to remove selected semiconductor layers (e.g., semiconductorlayers 208) in the PMOS region 501.

In some embodiments, the first removal process includes forming a firstpatterned resist layer by a lithography process over the substrate 202.The first patterned resist layer may include an opening exposing theNMOS region 500 while protecting the PMOS region 501. The first removalprocess may include a first etching process performed in the NMOS region500 through the opening of the patterned resist layer. In the example ofFIG. 9A, in the NMOS region 500, semiconductor layers 206 of the finelement 214A in the channel region 512 are completely removed. Thesemiconductor layers 208 of the fin element 214A remain substantiallyun-etched. In the following discussion, the portions of thesemiconductor layers 208 of the fin elements 214A in the channel regionsare referred to as the channel layers 908A. In the example of FIG. 9A,the channel layers 908A have a channel cross-sectional profile 904 of asquare and are suspended in the opening 804. Gaps 902A are formedbetween adjacent semiconductor layers 208. In some embodiments, thefirst etching process includes a selective wet etching process, and mayinclude a hydro fluoride (HF) etchant. After the first etching processis completed, the first patterned resist layer is removed.

In some embodiments, the second removal process includes forming asecond patterned resist layer by a lithography process over thesubstrate 202. The second patterned resist layer may include an openingexposing the PMOS region 501 while protecting the NMOS region 500. Thesecond removal process may include a second etching process performed inthe PMOS region 501 through the opening of the second patterned resistlayer. As illustrated in the example of FIG. 9A, in the PMOS region 501,semiconductor layers 208 of the fin element 214B in the channel region512 are partially removed to form supporting layers 910, which supportsemiconductor layers 206 in the channel region 512 (referred to as thechannel layers 908B hereafter). In the example of FIG. 9A, channellayers 908B have a channel cross-sectional profile 904 of a square.Adjacent channel layers 908B may be separated by a supporting layer 910and gaps 902B formed along opposing sidewalls of the supporting layer910. In some embodiments, a bottom surface of a channel layer 908B ofthe fin element 214B is substantially coplanar with a top surface of theSRB layer 204. In some embodiments, the second etching process includesa selective wet etching process, and may include a hydro fluoride (HF)etchant. After the second etching process is completed, the secondpatterned resist layer is removed.

Alternatively, in some embodiments, in the PMOS region 501, thesemiconductor layers 206 of the fin element 214B in the channel region512 are partially removed to form supporting layers 910, and thesemiconductor layers 208 of the fin element 214B in the channel region512 form channel layers 908B. In some examples, a bottom surface of asupporting layer 910 is substantially coplanar with a top surface of SRBlayer 204.

In some embodiments, in the PMOS region 501, the supporting layers 910are oxidized for isolation purposes. To further this embodiment, theoxidation process may include a wet oxidation process, a dry oxidationprocess, or a combination thereof. In one example, the device 200 isexposed to a wet oxidation process using water vapor or steam as theoxidant. In one example where the supporting layers 910 include SiGe,the oxidized supporting layers 910 include silicon germanium oxide.

Referring now to FIG. 9B, in some embodiments, channel layers 908A, 908Band/or supporting layers 910 are slightly etched to obtain variousdesirable dimensions and shapes in the channel region 512 by one or moreselective wet etching processes. In some examples, the selective wetetching process may be the same as the first and/or second wet etchingprocess used to remove selected semiconductor layers the NMOS region 500and PMOS region 501, or may include a separate etching process. In someembodiments, the etching conditions may be controlled so that thechannel layers 908A and 908B may have channel cross-sectional profilesof particular shapes, e.g., a rounded square, a circle, a diamond, anoval, or another geometrical shape. In the example of FIG. 9B, thechannel layers 908A and 908B have a profile 904 of the same shape (e.g.,a rounded square). Alternatively, in some examples, the channel layers908A and 908B may have profiles of different shapes. In someembodiments, the etching conditions of the etching process may becontrolled so that the channel layers 908A, 908B have desired channellayer widths 914 and desired channel layer heights 918, the supportinglayers 910 have desired supporting layer widths 916, and adjacentchannel layers 908A, 908B have desired spacing distances 912. Thevarious desired dimensions and shapes may be chosen based on deviceperformance considerations.

Referring now to FIG. 9C, in some embodiments, a capping layer 920including silicon may be grown around the channel layers 908A or 908B(e.g., when channel layers 908A or 908B have a Ge concentration in therange of about 30 atomic percent to about 100 atomic percent). Thecapping layer 920 may become a part of the channel layer 908A or 908B,and may affect the channel layer widths 914, channel layer heights 918,spacing distances 912, and profile 904. In some examples, the cappinglayer 920 has a thickness of about 0.5 nm to about 2 nm. By way ofexample, growth of the capping layer 920 may be performed by an MBEprocess, an MOCVD process, and/or other suitable epitaxial growthprocesses.

Referring to FIGS. 1B, 10A, 10B, and 10C, the method 150 proceeds toblock 112, where an interposing feature 1024 is formed in the channelregions of the fin elements. Referring to the examples of FIGS. 10A,10B, and 10C, in various embodiments, spacing distances 912 betweenadjacent channel layers 908A or 908B may affect the configurations ofthe interposing feature 1024 (e.g., portions of the interposing feature1024 disposed in the gaps 902A and 902B).

Referring now to the example of FIG. 10A, an interposing feature 1024 isformed over the substrate 202 in the channel regions 512. Portions ofthe interposing feature 1024 completely fill the gaps 902A, 902B to formspacing areas 1012A, 1012B.

In some embodiments, the interposing feature 1024 includes at least oneinterfacial layer 1002 disposed in the channel regions 512. In someembodiments, the interfacial layer 1002 has a thickness 1060 less thanor equal to about 1.5 nm. In some embodiments, the interfacial layer1002 has a thickness 1060 less than or equal to about 0.6 nm. In theexample of FIG. 10A, an interfacial layer 1002 completely wraps around achannel layer 908A of the fin element 214A, and a interfacial layer 1002partially wraps around a channel layer 908B of the fin element 214B.

In some embodiments, the interfacial layer 1002 may include anoxide-containing material such as silicon oxide or silicon oxynitride,and may be formed by chemical oxidation using an oxidizing agent (e.g.,hydrogen peroxide (H₂O₂), ozone (O₃)), plasma enhanced atomic layerdeposition, thermal oxidation, ALD, CVD, and/or other suitable methods.In some embodiments, the interfacial layer 1002 of the fin element 214Aand the interfacial layer 1002 of the fin element 214B include the samematerial. In some embodiments, interfacial layers 1002 of the finelements 214A and 214B may be formed separately and include differentmaterials. In some embodiments, a cleaning process, such as an HF-lastpre-gate cleaning process (for example, using a hydrofluoric (HF) acidsolution), may be performed before the interfacial layer 1002 is formedin the opening 804.

In some embodiments, the interposing feature 1024 includes at least onehigh-k dielectric layer 1004 of a high-k dielectric material disposedover and/or around the interfacial layer 1002 in the opening 804. Insome embodiments, the high-k dielectric layer 1004 may have a thickness1062 of about 0.5 nm to about 5 nm. In the example of FIG. 10A, a high-kdielectric layer 1004 completely wraps around a channel layer 908A ofthe fin element 214A, and a high-k dielectric layer 1004 partially wrapsaround a channel layer 908B. In some embodiments, the high-k dielectriclayers 1004 of fin elements 214A and 214B include the same material. Insome embodiments, the high-k dielectric layers 1004 of the fin elements214A and 214B are formed separately and include different materials.

In some embodiments, the high-k dielectric material has a highdielectric constant, for example, greater than that of thermal siliconoxide (˜3.9). The high-k dielectric material may include hafnium oxide(HfO₂), zirconium oxide (ZrO₂), lanthanum oxide (La₂O₃), aluminum oxide(Al₂O₃), titanium oxide (TiO₂), yttrium oxide, strontium titanate,hafnium oxynitride (HfO_(x)N_(y)), other suitable metal-oxides, orcombinations thereof. The high-k dielectric layer 1004 may be formed byALD, chemical vapor deposition (CVD), physical vapor deposition (PVD),remote plasma CVD (RPCVD), plasma enhanced CVD (PECVD), metal organicCVD (MOCVD), sputtering, other suitable processes, or combinationsthereof.

In some embodiments, the interposing feature 1024 includes at least onecapping layer 1006 of a capping material disposed over and/or around thehigh-k dielectric layer 1004 in the opening 804. The capping layer 1006may have a thickness 1064 of about 0.5 nm to about 5 nm. The cappingmaterial may include titanium nitride, tantalum nitride, tantalumcarbide, other suitable materials, and/or a combination thereof. Thecapping material may be formed by ALD and/or other suitable methods.Alternatively, in some embodiments, the interposing feature 1024 doesnot include a capping layer.

In some embodiments, a sidewall of the interposing feature 1024 has athickness 1028 of about 1 nm to about 6 nm, which may equal to acombined thickness of the thickness 1060 of the interfacial layer 1002,the thickness 1062 of high-k dielectric layer 1004, and the thickness1064 of the capping layer 1006 if any.

In the example of FIG. 10A, the spacing distance 912 is equal to or lessthan twice of the combined thickness of the interfacial layer 1002 andthe high-k dielectric layer 1004. As illustrated in FIG. 10A, for thefin element 214A, the spacing area 1012A is completely filled byportions of two interfacial layers 1002 and two high-k dielectric layers1004, where the two high-k dielectric layers 1004 merge in the spacingarea 1012A. For the fin element 214B, each of the two spacing areas1012B along a supporting layer 910 is completely filled by portions ofan interfacial layer 1002 and a high-k dielectric layer 1004.

Referring now to the example of FIG. 10B, where the spacing distance 912is greater than twice of the combined thickness of the interfacial layer1002 and high-k dielectric layer 1004, but equal to or less than twiceof the thickness 1028 of the interposing feature 1024. As illustrated inFIG. 10B, for the fin element 214A, the spacing area 1012A is completelyfilled by portions of two interfacial layers 1002, two high-k dielectriclayers 1004, and two capping layers 1006, where the two capping layers1006 merge in the spacing area 1012A. For the fin element 214B, each ofthe spacing areas 1012B along a supporting layer 910 is completelyfilled by portions of an interfacial layer 1002, a high-k dielectriclayer 1004, and a capping layer 1006.

Referring now to the example of FIG. 10C, illustrated are fin elements214A and 214B having a spacing distance 912 greater than twice of thethickness 1028 of the interposing feature 1024. As illustrated in FIG.10C, the spacing area 1012A is partially filled by portions of twointerfacial layers 1002, two high-k dielectric layers 1004, and twocapping layers 1006. In the example of FIG. 10C, for the fin element214A, the spacing area 1012A includes a gap 1066A disposed between theportions of the two capping layers 1006. For the fin element 214B, eachof the two spacing areas 1012B along opposing sides of the supportinglayer 910 is partially filled by portions of an interfacial layer 1002,a high-k dielectric layer 1004, and a capping layer 1006, and includes agap 1066B disposed between portions of the capping layer 1006 in thespacing area 1012B.

Referring now to FIGS. 1B and 11A, 11B, and 11C, the method 150 proceedsto block 164, where a scavenging metal layer is deposited in the channelregion of the fin elements. Referring to the examples of FIGS. 11A, 11B,and 11C, in various embodiments, spacing distances 912 between adjacentchannel layers 908A, 908B may be different, which may affect theconfigurations of the scavenging layer 1102 (e.g., portions of thescavenging layer 1102 disposed in the gaps 902A and 902B). In someexamples, the spacing areas 1012A and 1012B do not include anyscavenging material. In some examples, the spacing areas 1012A and 1012Binclude portions of at least one scavenging layer 1102.

Referring to the examples of FIGS. 11A and 11B, illustrated areembodiments of a device 200 of FIGS. 10A and 10B respectively after ascavenging metal layer 1102 is disposed in the opening 804, where thespacing distances 912 are equal to or less than twice the thickness 1028of the interposing feature 1024. In the examples of FIGS. 11A and 11B, ascavenging metal layer 1102 at least partially wraps around theinterposing feature 1024 of the fin elements 214A, 214B. In someembodiments, the scavenging metal layer 1102 may have a thickness 1104of about 0.5 nm to about 6 nm. The scavenging metal layer 1102 mayinclude a scavenging material, such as titanium, hafnium, zirconium,tantalum, titanium nitride, tantalum nitride, tantalum silicon nitride,titanium silicon nitride, other suitable material, or combinationsthereof. The scavenging material may be configured to facilitate ascavenging process on the interfacial layer 1002. In the examples ofFIGS. 11A and 11B, the spacing areas 1012A and 1012B are free of thescavenging material.

Referring to the example of FIG. 11C, illustrated is embodiments of adevice 200 of FIG. 10C after a scavenging metal layer 1102 is disposedin the opening 804, where the spacing distances 912 are greater thantwice of the thickness 1028 of the interposing feature 1024. Asillustrated in the example of FIG. 11C, the spacing area 1012A includesthe portions of the two scavenging metal layers 1102, which at leastpartially fill the gap 1006A of the fin element 214A. In the examples ofFIG. 11C, the spacing areas 1012B include portions of the scavengingmetal layer 1102, which at least partially fill the gaps 1006B in thespacing areas 1012B.

In some embodiments, the scavenging metal layer 1102 may be formed byALD, chemical vapor deposition (CVD), physical vapor deposition (PVD),remote plasma CVD (RPCVD), plasma enhanced CVD (PECVD), metal organicCVD (MOCVD), sputtering, other suitable processes, or combinationsthereof.

Referring to FIGS. 1, 12A, 12B, 12C, 12D, 13A, 13B, and 13C, the method150 proceeds to block 166, where a scavenging process is performed onthe interfacial layer 1002 to form a treated interfacial layer 1202.Referring to the examples of FIGS. 12A and 12C, one or more annealingprocesses may be performed to cause a scavenging process to theinterfacial layer 1002.

In various embodiments, the annealing processes may comprise rapidthermal annealing (RTA), laser annealing processes, or other suitableannealing processes. As an example, the annealing processes may includea high temperature thermal annealing step that may apply temperatures inthe range of about 600° C. and 1000° C., though other embodiments mayuse temperatures within a different range.

In various embodiments, a scavenging process may be used to improvedevice performance. For example, the scavenging process may be used toreduce the EOT of the gate structure. For further example, thescavenging process may be used to reduce interface dipole between theinterfacial layer 1002 and high-k dielectric layer 1004, so that theflat band voltage V_(fb) and/or threshold voltage V_(t) of the device200 may be tuned. For further example, the scavenging process may helpincrease the threshold voltage V_(t) by a voltage in the range of about50 millivolt to about 200 millivolt.

To achieve the desired device performance improvements, in someembodiments, all areas of the interfacial layer 1002 are scavengedduring the scavenging process to form a treated interfacial layer 1202that is uniform. Un-scavenged areas may cause non-uniformity of thetreated interfacial layer 1202, which may create issues associated withnon-uniform device turn on or effective area reduction in the gatestructure. In some examples, a particular area of the interfacial layer1002 is not scavenged during the scavenging process because theparticular area has a distance to the scavenging layer 1202 (alsoreferred to as a scavenging distance) greater than a predeterminedscavenging threshold T (e.g., 6 nm).

In various embodiments, uniformity of the treated interfacial layer 1202may be affected by the greatest scavenging distance of all areas of theinterfacial layer 1002, which is also referred to as a maximumscavenging distance of the interfacial layer 1002. To ensure that allareas of the interfacial layer 1002 are scavenged for form a treatedinterfacial layer 1202 that is uniform, it may be designed that amaximum scavenging distance 1258 of the interfacial layer 1002 is equalto or less than the predetermined scavenging threshold T.

Referring to the examples of FIGS. 12A and 12B, in some embodiments, allareas of an interfacial layer 1002 are scavenged to form a uniformtreated interfacial layer 1202. As illustrated in FIG. 12A, a scavenginglayer 1102 completely wraps around the interfacial layer 1002, and themaximum scavenging distance 1258 (e.g., equal to a thickness 1028 of theinterposing feature 1024) is less than a predetermined scavengingthreshold T. As illustrated in FIG. 12B, all areas of the interfaciallayer 1002 are scavenged to form a uniform treated interfacial layer1202. The treated interfacial layer 1202 may include a first layer 1204.In some examples, the first layer 1204 is an epitaxially grown siliconlayer, and may become a part of the channel layer 908.

In some embodiments, the interfacial layer 1002 may be fully convertedto the first layer 1204 (e.g., by adjusting the scavenging metal layer1102's oxygen affinity and/or annealing parameters). In one example, thefirst layer 1024 has a thickness 1250 that is about the same as thethickness 1060 of the interfacial layer 1002. The final EOT of thedielectric stack may be defined solely by the EOT of the high-kdielectric layer 1004.

Alternatively, as illustrated in the example of FIG. 12B, in someembodiments, the treated interfacial layer 1202 may include a secondlayer 1206 with a thickness 1252 less than the thickness 1060 of theinterfacial layer 1002 (e.g., by adjusting the scavenging metal layer1102's oxygen affinity and/or annealing parameters). In some examples,the second layer 1206 includes the same material as the material of theinterfacial layer 1002. The final EOT of the dielectric stack may bedefined by the EOT of the second layer 1206 and the EOT of the high-kdielectric layer 1004.

Referring to the examples of FIGS. 12C and 12D, in some embodiments,some areas of an interfacial layer 1002 are not scavenged during thescavenging process. As illustrated in FIG. 12C, the scavenging metallayer 1102 includes gaps 1254, and does not uniformly wrap around theinterfacial layer 1002. The maximum scavenging distance 1258 equals to ascavenging distance of areas 1208, and is greater than a predeterminedscavenging threshold T. As such, areas 1208 are not scavenged during thescavenging process. Referring now to the example of FIG. 12D, thetreated interfacial layer 1202 includes un-scavenged areas 1208, whichaffects the uniformity of the treated interfacial layer 1202. In someembodiments, the un-scavenged areas 1208 extend between the first layer1204 and second layer 1206. In the example of FIG. 12D, the final EOT ofthe dielectric stack may be affected by the second layer 1206, theun-scavenged areas 1208, and the EOT of the high-k dielectric layer1004.

Referring now to FIGS. 13A, 13B, and 13C, in some embodiments, themaximum scavenging distance 1258 of an interfacial layer 1002 of a finelement may be affected by the spacing distance 912 between adjacentchannel layers and/or channel cross-sectional profiles 904 of thechannel layers. It is noted that to simplify discussion, in the exampleof FIGS. 13A, 13B, and 13C, the interposing features 1024 of the finelements 1314A, 1314B, 1314C have the same thickness 1028 (e.g., Y6),and the channel layers 908 of the fin elements 1314A, 1314B, 1314C havethe same channel layer widths 914 (e.g., W1) and channel layer heights918 (e.g., W1). While the channel cross-sectional profiles discussedhere are of shapes including a square, a rounded square, and a circle,it will be understood that channel cross-sectional profiles of othershapes (e.g., a diamond, an oval, a rectangle) are possible, and areintended to fall within the scope of the present disclosure.

Referring to FIG. 13A, exemplary curves 1302, 1304, and 1306 illustratemaximum scavenging distances 1258 as a function of spacing distances 912and channel cross-sectional profiles 904. Particularly, curves 1302,1304, and 1306 correspond to fin elements 1314A, 1314B, 1314C havingchannel cross-sectional profiles 904 of a square, a rounded square, anda circle respectively. In FIG. 13A, the horizontal axis “X” representsthe spacing distance 912, and the vertical axis “Y” represents themaximum scavenging distance 1258 of the interfacial layer 1002. Asillustrated in FIG. 13A, the fin elements 1314A, 1314B, 1314C withvarious channel cross-sectional profiles may have different maximumscavenging distances 1258 at a particular spacing distance between X1and X4. In some embodiments, X4 is equal to twice the thickness 1028(e.g., Y6) of the interposing feature 1024.

Referring now to the examples of FIGS. 13B and 13C, simplified finelements 1314A, 1314B, and 1314C further illustrate that maximumscavenging distances 1258 may be affected by the channel cross-sectionalprofiles 904 of channel layers 908.

As shown in the examples of FIGS. 13B and 13C, the maximum scavengingdistance 1258 may increase when the spacing distance 912 decreases. Inthe example of FIG. 13B, the fin element 1314A has a spacing distance912 (e.g., greater than twice of Y6) so that its spacing area 1012Aincludes a portion of the scavenging metal layer 1102 disposed directlyunder the area A of the interfacial layer 1002. Thus, the fin element1314A has a maximum scavenging distance 1258 (e.g., Y6) extendingvertically from the area A to the inner surfaces 1364 of the scavengingmetal layer 1102. Referring now to the example of FIG. 13C, as thespacing distance 912 of the fin elements 1314A decreases (e.g., to lessthan twice of Y6), the spacing area 1012A becomes smaller, and there isno scavenging layer 1102 disposed directly under the area A. Thus, themaximum scavenging distance 1258 of the fin element 1314A increases, andextends from the area A to the scavenging metal layers 1102 in adirection at an angle θ₁ (e.g., 90 degrees) with the vertical line.

Similarly, as shown in the example of FIG. 13C, the maximum scavengingdistances 1258 of fin elements 1314B and 1314C may also increase as thespacing distance 912 decreases. However, because of the differentchannel cross-sectional profiles, the respective maximum scavengingdistances 1258 may extend from areas B, and C to the scavenging metallayers 1102 in different directions (e.g., at angles θ₂, and θ₃ with thevertical line respectively, where θ₂ may be less than θ₁, and/or θ₃ maybe less than θ₂), and have different values. For example, the maximumscavenging distance 1258 of the fin element 1314C having a circle shapedcross-sectional profile may be less than the maximum scavengingdistances 1258 of both the fin elements 1314A and 1314B.

In some embodiments, the spacing distances 912 and/or channelcross-sectional profiles 904 may be chosen based a predeterminedscavenging threshold T used in the scavenging process based on deviceperformance considerations (e.g., channel semiconductor layers density,scavenging uniformity, EOT thickness, and/or V_(fb) and/or V_(t)tuning).

Referring back to FIG. 13A, three scavenging thresholds T1, T2, and T3are illustrated. The scavenging threshold T1 is greater than Y1, thescavenging threshold T2 (the same as Y3) is between Y1 and Y6, and thescavenging threshold T3 is less than Y6.

In some embodiments where the scavenging process uses the scavengingthreshold T1, all areas of the interfacial layers 1002 of all finelements 1314A, 1314B, and 1314C may be scavenged regardless of thespacing distance and channel cross-sectional profile to form treatedinterfacial layers 1202 that do not include any un-scavenged areas 1208.

Alternatively, in some embodiments where the scavenging process uses thescavenging threshold T3, for each of the fin elements 1314A, 1314B, and1314C, at least an area 1208 of an interfacial layer 1002 is notscavenged regardless of the spacing distance and channel cross-sectionalprofile, and the treated interfacial layer 1202 includes theun-scavenged area 1208, which affects the uniformity of the treatedinterfacial layer 1202.

Alternatively, in some embodiments where the scavenging process uses thescavenging threshold T2 that is greater than Y6 but less than Y1,spacing distances 912 and/or channel cross-sectional profiles 904 may bechosen to form a treated interfacial layer 1202 that is uniform (e.g.,not including any un-scavenged areas 1208) based on the scavengingthreshold T2 and/or desired channel layer density. As shown in FIG. 13A,the minimum spacing distance to ensure that all areas of the interfaciallayer 1002 are scavenged is X4, X2, and X6 for fin elements 1314A,1314B, and 1314C respectively. Because X6 is less than X2, which is lessthan X4, the fin element 1314C may have a greater channel layer densitythan the fin element 1314B, which may have a greater channel layerdensity than the fin element 1314A.

In some embodiments, the maximum scavenging distance 1258 of theinterfacial layer 1002 may be affected by other parameters (e.g., widthof supporting layers 910).

Referring now to the examples of FIGS. 14A, 14B, and 14C, illustrated isa device 200 with fin elements 214A and 214B of various spacingdistances with rounded square channel cross-sectional profiles after ascavenging process is performed. In some examples, one or both of thefin elements 214A and 214B correspond to the curve 1304 of FIG. 13A.

Referring now to the examples of FIG. 14A, the fin elements 214A and214B have a spacing distance 912 of X6 and a maximum scavenging distance1258 of Y7. As illustrated in FIGS. 13A and 14A, because the maximumscavenging distance Y7 of the interfacial layer 1002 is greater than thescavenging threshold T2, in some embodiments, areas 1208 of theinterfacial layer 1002 are not scavenged during the scavenging process,and the treated interfacial layer 1202 includes un-scavenged areas 1208.

In the examples of FIG. 14B, the fin elements 214A and 214B have aspacing distance 912 of X3 less than X4 and a maximum scavengingdistance 1258 of Y4. As illustrated in FIGS. 13A and 14B, because themaximum scavenging distance Y4 of the interfacial layer 1002 is lessthan the scavenging threshold T2, all areas of the interfacial layer1002 are scavenged during the scavenging process, and the treatedinterfacial layer 1202 does not include any un-scavenged areas 1208.

In the examples of FIG. 14C, the fin elements 214A and 214B have aspacing distance 912 of X5 greater than X4 and a maximum scavengingdistance 1258 of Y6. As illustrated in FIGS. 13A and 14C, because themaximum scavenging distance Y6 of the interfacial layer 1002 is lessthan the scavenging threshold T2, all areas of the interfacial layer1002 are scavenged during the scavenging process, and the treatedinterfacial layer 1202 does not include any un-scavenged areas 1208.

In some embodiments, after the scavenging process is performed, thescavenging metal layer 1102 may be removed by using a suitable etchingprocess (e.g., dry or wet etching).

Referring now to FIGS. 1 and 15, the method 150 proceeds to block 168,where a metal layer is formed over the substrate 202. For ease ofreference, the interposing feature 1024 and scavenging metal layer 1102are omitted in the gate stack 1506 in FIG. 15, and the ILD layer 702,CESL 704, and the dielectric layer 708 are also omitted in FIG. 15.

Referring to the example of FIG. 15, gate stacks 1506 may be formed inthe channel regions of the fin elements 214A and 214B may be a portionof a first device 1502A and a second device 1502B respectively. The gatestack 1506 may include a gate metal layer 1508 disposed in the channelregions 512. The gate metal layer 1508 may include a single layer oralternatively a multi-layer structure, such as various combinations of ametal layer with a selected work function to enhance the deviceperformance (work function metal layer), a liner layer, a wetting layer,an adhesion layer, a metal alloy or a metal silicide. By way of example,the gate metal layer 1508 of the gate stack 1506 may include Ti, Ag, Al,TiAlN, TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru, Mo, Al, WN, Cu, W, Re,Ir, Co, Ni, other suitable metal materials or a combination thereof. Invarious embodiments, the gate metal layer 1508 of the gate stack 1506may be formed by ALD, PVD, CVD, e-beam evaporation, or other suitableprocess. Further, the gate metal layer 1508 may be formed separately forN-FET (e.g., fin element 214A) and P-FET transistors (e.g., fin element214B) which may use different metal layers. In various embodiments, aCMP process may be performed to remove excessive metal from the gatemetal layer 1508 of the gate stack 1506, and thereby provide asubstantially planar top surface of the gate metal layer 1508 of thegate stack 1506. In addition, the gate metal layer 1508 may provide anN-type or P-type work function, may serve as a transistor (e.g., FINFET)gate electrode, and in at least some embodiments, the gate metal layer1508 may include a polysilicon layer.

The semiconductor device 200 may undergo further processing to formvarious features and regions known in the art. For example, subsequentprocessing form contact openings, contact metal, as well as variouscontacts, vias, wires, and multilayer interconnect features (e.g., metallayers and interlayer dielectrics) on the substrate 202, configured toconnect the various features to form a functional circuit that mayinclude one or more multi-gate devices. In furtherance of the example, amultilayer interconnection may include vertical interconnects, such asvias and contacts, and horizontal interconnects, such as metal lines.The various interconnection features may employ various conductivematerials including copper, tungsten, and/or silicide. In one example, adamascene and/or dual damascene process is used to form a copper relatedmultilayer interconnection structure. Moreover, additional process stepsmay be implemented before, during, and after the method 150, and someprocess steps described above may be replaced or eliminated inaccordance with various embodiments of the method 150.

The embodiments of the present disclosure offer advantages over existingart, although it is understood that different embodiments may offerdifferent advantages, not all advantages are necessarily discussedherein, and that no particular advantage is required for allembodiments. By utilizing the disclosed method and structure,interfacial layers on/around vertically stacked nanowires may bescavenged uniformly without requiring scavenging metal layers disposedbetween the vertically adjacent nanowires, which may reduce nanowirespacing requirement and increase nanowire density. In one example, thenanowires may be shaped to have a cross-sectional profile of apredetermined shape based on a scavenging threshold and/or desirednanowire density, such that all areas of the interfacial layers may bescavenged during the scavenging process to form a uniformly treatedinterfacial layer. By uniformly scaling down the interfacial layer, theEOT of the dielectric stack can be improved, and the flat band voltageV_(fb) and/or threshold voltage V_(t) may be uniformly tuned, which inturn can improve overall device performance.

Thus, one aspect of the present disclosure involves a method of forminga semiconductor device. A fin extending from a substrate is provided.The fin has a source/drain region and a channel region, and includes afirst layer disposed over the substrate, a second layer disposed overthe first layer, and a third layer disposed over the second layer. Atleast a portion of the second layer is removed from the channel regionto form a gap between the first and third layers. A first material isformed in the channel region to form a first interfacial layer portionat least partially wrapping around the first layer and a secondinterfacial layer portion at least partially wrapping around the thirdlayer. A second material is deposited in the channel region to form afirst high-k dielectric layer portion at least partially wrapping aroundthe first interfacial layer portion and a second high-k dielectric layerportion at least partially wrapping around the second interfacial layerportion. A metal layer including scavenging material is formed alongopposing sidewalls of the first and second high-k dielectric layerportions in the channel region.

Another aspect of the present disclosure involves a method includingforming a fin element including first, second, and third semiconductorlayers. At least a portion of the second semiconductor layer is removedfrom a channel region of the fin element to form a gap between the firstand third layers. An interposing feature is formed in the channelregion. The interposing feature includes a first interfacial layerportion at least partially wrapping around the first semiconductorlayer, a first high-k dielectric layer portion at least partiallywrapping around the first interfacial layer portion, a secondinterfacial layer portion at least partially wrapping around the secondsemiconductor layer, and a second high-k dielectric layer portion atleast partially wrapping around the second interfacial layer portion. Ametal layer at least partially wrapping around the interposing featureis deposited. The metal layer includes a scavenging material.

Yet another aspect of the present disclosure involves a semiconductordevice. The semiconductor device includes a fin element extending from asubstrate. A channel region of the fin element includes a firstsemiconductor layer, a second semiconductor layer disposed over thefirst semiconductor layer and vertically separated from the firstsemiconductor layer by a spacing area, a first high-k dielectric layerportion at least partially wrapping around the first semiconductorlayer, a second high-k dielectric layer portion at least partiallywrapping around the second semiconductor layer, and a metal layer formedalong opposing sidewalls of the first and second high-k dielectric layerportions. The metal layer includes a scavenging material, and thespacing area is free of the scavenging material.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a finextending from a substrate, the fin having a source/drain region and achannel region, wherein the channel region includes: a firstsemiconductor layer; a second semiconductor layer disposed over thefirst semiconductor layer and vertically separated from the firstsemiconductor layer by a spacing area extending from a top surface ofthe first semiconductor layer to a bottom surface of the secondsemiconductor layer; a third semiconductor layer including silicon atleast partially wrapping around the second semiconductor layer; a high-kdielectric layer at least partially wrapping around the firstsemiconductor layer and the second semiconductor layer; and a metallayer formed along opposing sidewalls of the high-k dielectric layer,wherein the metal layer includes a first material, and wherein thespacing area is free of the first material.
 2. The semiconductor deviceof claim 1, wherein each of the first and second semiconductor layershas a rounded profile.
 3. The semiconductor device of claim 2, whereinthe rounded profile has a circle shape.
 4. The semiconductor device ofclaim 1, wherein the second semiconductor layer includes at least one ofsilicon germanium and germanium.
 5. The semiconductor device of claim 1,wherein the channel region further includes: a fourth semiconductorlayer disposed between the first and second semiconductor layers,wherein a top surface of the fourth semiconductor layer interfaces atleast a portion of the bottom surface of the second semiconductor layer;and wherein a bottom surface of the fourth semiconductor layerinterfaces at least a portion of the top surface of the firstsemiconductor layer.
 6. The semiconductor device of claim 5, wherein thefourth semiconductor layer includes silicon germanium oxide.
 7. Thesemiconductor device of claim 1, wherein the third semiconductor layerhas a thickness between 0.5 nm and 2 nm.
 8. A semiconductor device,comprising: a fin extending from a substrate, wherein a channel regionof the fin includes: a first semiconductor layer; a second semiconductorlayer disposed over the first semiconductor layer and verticallyseparated from the first semiconductor layer by a spacing area; a thirdsemiconductor layer including silicon at least partially wrapping aroundthe second semiconductor layer; an interposing feature including: afirst portion of a continuous first material layer at least partiallywrapping around the first semiconductor layer; a second portion of thecontinuous first material layer at least partially wrapping around thesecond semiconductor layer; and a metal layer formed along opposingsidewalls of the interposing feature in the channel region, wherein thespacing area is free of the metal layer.
 9. The semiconductor device ofclaim 8, wherein each of the first and second semiconductor layers has arounded profile.
 10. The semiconductor device of claim 8, wherein thesecond semiconductor layer includes at least one of silicon germaniumand germanium.
 11. The semiconductor device of claim 8, wherein athickness of the first semiconductor layer is less than twice of a widthof the interposing feature.
 12. The semiconductor device of claim 8,wherein the channel region further includes: a fourth semiconductorlayer disposed between the first and second semiconductor layers,wherein a top surface of the fourth semiconductor layer interfaces abottom surface of the second semiconductor layer; and wherein a bottomsurface of the fourth semiconductor layer interfaces a top surface ofthe first semiconductor layer.
 13. The semiconductor device of claim 12,wherein the fourth semiconductor layer includes silicon germanium oxide.14. The semiconductor device of claim 9, wherein the rounded profile isselected from the group consisting of a rounded square, a circle, and anoval.
 15. A semiconductor device, comprising: a fin element extendingfrom a substrate, wherein a channel region of the fin element includes:a first semiconductor layer; a second semiconductor layer disposed overthe first semiconductor layer and vertically separated from the firstsemiconductor layer by a spacing area; a third semiconductor layerdisposed between the first and second semiconductor layers, wherein atop surface of the third semiconductor layer interfaces a bottom surfaceof the second semiconductor layer; and wherein a bottom surface of thethird semiconductor layer interfaces a top surface of the firstsemiconductor layer; a fourth semiconductor layer including silicon atleast partially wrapping around the second semiconductor layer; a high-kdielectric layer at least partially wrapping around the first, second,and third semiconductor layers; and a metal layer formed along opposingsidewalls of the high-k dielectric layer, wherein the metal layerincludes a scavenging material, and wherein the spacing area is free ofthe scavenging material.
 16. The semiconductor device of claim 15,wherein each of the first and second semiconductor layers has a roundedprofile.
 17. The semiconductor device of claim 16, wherein the roundedprofile has a rounded square shape.
 18. The semiconductor device ofclaim 15, wherein the second semiconductor layer includes at least oneof silicon germanium and germanium.
 19. The semiconductor device ofclaim 15, wherein the third semiconductor layer includes silicongermanium oxide.
 20. The semiconductor device of claim 15, wherein thescavenging material includes at least one of titanium, hafnium,zirconium, tantalum, titanium nitride, tantalum nitride, tantalumsilicon nitride, and titanium silicon nitride.